[Cost-effectiveness study of olanzapine pamoate: Mirror-image analysis after one year]

Olanzapine pamoate has a higher cost of treatment than the oral form and requires administration in a hospital setting (unlike other long-acting antipsychotics), and the cost-effectiveness of this treatment may be questioned. Many scientific societies and national health systems are increasingly interested in the pharmacoeconomic impact of health products. The search for efficacy of a treatment can be done in two ways: medico-economic modeling studies or observational studies i.e. randomized controlled trials or mirror studies. The models are based on theoretical models from published clinical data simulating the course and evolution of patient health conditions, which benefit from a particular therapeutic strategy. Even if the design of observational mirror studies makes it possible to get closer to the clinical reality by observing the patient before and after the initiation of the treatment, the majority of the pharmacoeconomic studies published on olanzapine pamoate are modeling works that do not reflect actual conditions of care. The Guillaume Régnier Hospital Center in Rennes has a large cohort of patients treated with olanzapine pamoate: 121 instauration treatments are recorded from April 1, 2010 to Mars 1, 2015. The objective of this study is to evaluate the cost-effectiveness of olanzapine pamoate in actual clinical practice.

This is a one-year cost-effectiveness retrospective observational mirror-image study of a cohort of 52 patients with schizophrenia who were treated for at least three months with olanzapine pamoate. The primary efficacy endpoint is the differential in the number of full-time hospitalizations before and after the introduction of olanzapine pamoate versus the hospital cost differential. The secondary criteria are the difference of the number of the days spent in hospital and the number of outpatient consultations between the year preceding the injection and the year following it. The results were calculated on the general cohort and within 2 subgroups: patients treated for more than one year and those receiving less than one year of treatment with olanzapine pamoate.

Fifty-two patients were included (median age=35 years, sex ratio H/F=2.7) and only 38.5% discontinued treatment. For patients who maintained long-acting treatment, they received a dosage of 25mg oral olanzapine (min=7.5mg, max=60mg), 5mg more medially than the group having stopped the olanzapine pamoate (20mg; min=10mg, max=40mg). The majority of these patients were receiving off-label authorized marketing doses of oral olanzapine, whereas 22% of them had off-label dosages of olanzapine pamoate. The main causes of discontinuation were symptom persistence, loss of vision and the occurrence of adverse effects (including weight gain and sedation). Olanzapine pamoate significantly reduced the number of hospitalizations compared to the previous management strategy (1 less hospitalization, P<0.001 in patients treated more than one year and in the general cohort). As a logical consequence the number of hospitalization days in day care increased after the establishment of this long-acting antipsychotic with hospital reserve status (18 in median; min=0, max=159). We observed a non-statistically significant tendency of decrease in the number of days of full-time hospitalization and an increase in the number of ambulatory procedures, particularly in patients who have maintained the treatment for one year. This efficiency had a non-significant additional cost of €3361 per year. There was an average multiplication by 8,5 of the drug cost a year later in the general cohort (5.5 in the group of patients treated less than one year and 10.4 in the group of patients who maintained it a year). There was a 23,2% average increase in the cost of hospitalization in the general cohort (3.75 % in patients who maintained treatment compared to 48.9% in patients who discontinued treatment).

By its mirror design, the study was placed in real conditions of care of the patient with schizophrenia. A total of 61.5% of patients maintained treatment with olanzapine pamoate for a minimum of one year. This APAP is more effective without significantly increasing the cost compared to the previous therapeutic strategy (including oral olanzapine). The additional cost is partly due to the administration restriction in a hospital setting in relation to risk of Post-Injection Delirium/Sedation Syndrom (PDSS). There is currently no acceptable efficiency limit. The results of this cost-effectiveness analysis cannot be extrapolated to the other long-acting antipsychotics since it is the only one with hospital reserve status. The current limitations of medico-economics in psychiatry derive from the heterogeneity of clinical forms and the management of mental pathologies.